Endpoint detector and method for measuring a change in wafer thickness in chemical-mechanical polishing of semiconductor wafers and other microelectronic substrates

ABSTRACT

An endpoint detector and performance monitoring system for quickly and accurately measuring the change in thickness of a wafer and other planarizing parameters in chemical-mechanical polishing processes. In one embodiment, an endpoint detector has a reference platform, a measuring face, and a distance measuring device. The reference platform is positioned proximate to the wafer carrier, and the reference platform and measuring device are positioned apart from one another by a known, constant distance. The measuring face is fixedly positioned with respect to the wafer carrier at a location that allows the measuring device to engage the measuring face when the wafer is positioned on the reference platform. Each time the measuring device engages the measuring surface, it measures the displacement of the measuring face with respect to the measuring device. The displacement of the measuring face is proportional to the change in thickness of the wafer between measurements. In another embodiment, a planarizing machine has a flat plate, a planarizing medium fastened to the plate, a carrier assembly to manipulate a substrate holder over the planarizing medium, and a non-contact distance measuring device. The non-contact distance measuring device measures the actual elevation of the substrate holder as the substrate holder engages a substrate with the planarizing medium and relative motion occurs between the substrate holder and the planarizing medium. The performance monitoring system uses the actual pad elevation to determine the endpoint, the polishing rate and other CMP operating parameters.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of U.S. application Ser. No. 08/602,617,filed on Feb. 16, 1996, now U.S. Pat. No. 5,777,739 allowed on Oct. 2,1997, and entitled "ENDPOINT DETECTOR AND METHOD FOR MEASURING A CHANGEIN WAFER THICKNESS IN CHEMICAL-MECHANICAL POLISHING OF SEMICONDUCTORWAFERS."

TECHNICAL FIELD

The present invention relates to an endpoint detector and a method forquickly and accurately measuring a change in thickness of asemiconductor wafer or another microelectronic substrate in mechanicalor chemical-mechanical polishing processes.

BACKGROUND OF THE INVENTION

Chemical-mechanical polishing or mechanical polishing processes(collectively "CMP") remove material from the surface of amicroelectronic substrate (e.g., a semiconductor wafer) in theproduction of ultra-high density integrated circuits. In a typical CMPprocess, a wafer is pressed against a planarizing medium (e.g., apolishing pad) in the presence of a planarizing fluid (e.g., an abrasiveslurry) under controlled chemical, pressure, velocity, and temperatureconditions. The planarizing fluid may contain small, abrasive particlesto abrade the surface of the wafer, but a non-abrasive planarizing fluidmay be used with fixed-abrasive polishing pads. Additionally, theplanarizing fluid has chemicals that etch and/or oxidize the surface ofthe wafer. The polishing pad is generally a planar pad made from aporous material, such as blown polyurethane, and it may also haveabrasive particles bonded to the material. Thus, when the pad and/or thewafer moves with respect to the other, material is removed from thesurface of the wafer by the abrasive particles (mechanical removal) andthe chemicals (chemical removal).

FIG. 1 schematically illustrates a conventional CMP machine 10 with aplaten 20, a wafer carrier 30, a polishing pad 40, and a slurry 44 onthe polishing pad. The platen 20 has a surface 22 upon which thepolishing pad 40 is positioned. A drive assembly 26 rotates the platen20 as indicated by arrow "A". In another type of existing CMP machine,the drive assembly 26 reciprocates the platen back and forth asindicated by arrow "B". The motion of the platen 20 is imparted to thepad 40 because the polishing pad 40 frictionally engages the surface 22of the platen 20. The wafer carrier 30 has a lower surface 32 to which awafer 60 may be attached, or the wafer 60 may be attached to a resilientpad 34 positioned between the wafer 60 and the lower surface 32. Thewafer carrier 30 may be a weighted, free-floating wafer carrier, or anactuator assembly 36 may be attached to the wafer carrier 30 to impartaxial and rotational motion, as indicated by arrows "C" and "D",respectively.

In the operation of the conventional polisher 10, the wafer 60 ispositioned face-downward against the polishing pad 40, and then theplaten 20 and the wafer carrier 30 move relative to one another. As theface of the wafer 60 moves across the planarizing surface 42 of thepolishing pad 40, the polishing pad 40 and the slurry 44 remove materialfrom the wafer 60.

In the competitive semiconductor industry, it is highly desirable tomaximize the throughput of CMP processes to produce accurate, planarsurfaces as quickly as possible. The throughput of CMP processes is afunction of several factors, one of which is the ability to accuratelystop the CMP process at a desired endpoint. Accurately stopping the CMPprocess at a desired endpoint is important to maintaining a highthroughput because the thickness of the dielectric layer must be withinan acceptable range; if the thickness of the dielectric layer is notwithin an acceptable range, the wafer must be re-polished until itreaches the desired endpoint. Re-polishing a wafer, however,significantly reduces the throughput of CMP processes. Thus, it ishighly desirable to stop the CMP process at the desired endpoint.

In one conventional method for determining the endpoint of the CMPprocess, the polishing period of one wafer in a run is estimated usingthe polishing rate of previous wafers in the run. The estimatedpolishing period for the wafer, however, may not be accurate because thepolishing rate may change from one wafer to another. Thus, this methodmay not accurately polish the wafer to the desired endpoint.

In another method for determining the endpoint of the CMP process, thewafer is removed from the pad and wafer carrier, and then the thicknessof the wafer is measured. Removing the wafer from the pad and wafercarrier, however, is time-consuming and may damage the wafer. Moreover,if the wafer is not at the desired endpoint, then even more time isrequired to re-mount the wafer to the wafer carrier for repolishing.Thus, this method generally reduces the throughput of the CMP process.

In still another method for determining the endpoint of the CMP process,a portion of the wafer is moved beyond the edge of the pad, and aninterferometer directs a beam of light directly onto the exposed portionof the wafer. The wafer, however, may not be in the same referenceposition each time it overhangs the pad because the edge of the pad iscompressible, the wafer may pivot when it overhangs the pad, and theexposed portion of the wafer may vary from one measurement to the next.Thus, this method may inaccurately measure the change in thickness ofthe wafer.

In light of the problems with conventional endpoint detectiontechniques, it would be desirable to develop an apparatus and a methodfor quickly and accurately measuring the change in thickness of a waferduring the CMP process.

In addition to accurately determining the endpoint of CMP processes, itis also desirable to monitor other performance characteristics orparameters to maintain the throughput and quality of finished wafers.The performance of CMP processes may be affected by the pad condition,the distribution of planarizing fluid under the wafer, and many otherplanarizing parameters. Monitoring these parameters, however, isdifficult because it is time consuming to interrupt processing wafers todetermine whether one of the parameters has changed. Moreover, if theCMP process is stopped and all of the parameters appear to be in anacceptable range, it is a complete waste of processing time. Thus, itwould also be desirable to monitor the performance of CMP processing toensure that the planarizing parameters are within acceptable operatingranges without interrupting the process.

SUMMARY OF THE INVENTION

The invention is directed, in part, to detecting the endpoint of aplanarization process that removes material from a microelectronicsubstrate, such as a semiconductor wafer. An endpoint detector measuresthe change in thickness of a semiconductor wafer while the wafer isattached to a wafer carrier during chemical-mechanical polishing of thewafer. The endpoint detector has a reference platform, a measuring face,and a distance measuring device. The reference platform is positionedproximate to the wafer carrier, and the reference platform and measuringdevice are positioned apart from one another by a known, constantdistance for all of the measurements of a single wafer. The measuringface is fixedly positioned with respect to the wafer carrier at alocation that allows the measuring device to engage the measuring facewhen the wafer is positioned on the reference platform. Each time themeasuring device engages the measuring surface, it measures thedisplacement of the measuring face with respect to the measuring device.The displacement of the measuring face is proportional to the change inthickness of the wafer between measurements.

In a method in accordance with the invention, the wafer is placed on thereference platform before it is polished, and then the measuring deviceengages the measuring surface to determine a baseline measurement of theposition of the measuring face with respect to the measuring device.After the wafer is at least partially polished, the wafer is re-placedon the reference platform and the measuring device is re-engaged withthe measuring face to determine a subsequent measurement of the positionof the measuring face with respect to the measuring device. Thedisplacement of the measuring face from the baseline measurement to thesubsequent measurement is proportionate to the change in thickness ofthe wafer.

The invention is also directed towards planarizing machines and methodsfor monitoring the polishing rate, endpoint, and other planarizingparameters of CMP processes. A planarizing machine in accordance withthe invention includes a flat plate, a planarizing medium fastened tothe plate, a carrier assembly to manipulate a substrate with respect tothe planarizing medium, and a non-contact distance measuring device. Thecarrier assembly, more specifically, may have a support structure and asubstrate holder coupled to the support structure. The substrate holdertypically has a mounting site facing the planarizing medium to carry thesubstrate, and a backside facing away from the planarizing medium. Thenon-contact distance measuring device may also be attached to thesupport structure to be positioned over the substrate holder for atleast a portion of the planarizing process. Additionally, the supportstructure typically holds the non-contact measuring device at a knownelevation with respect to the plate to measure an actual distancebetween the backside of the substrate holder and the known elevationwhile the substrate is planarized.

The distance measuring device may have a beam emitter that projects asource beam, a reflector positioned at a predetermined angle withrespect to the plate to direct the source beam against the backside ofthe substrate holder, and a primary detector to receive a return beamreflected from the backside of the substrate holder normal to the sourcebeam. The primary detector monitors a lateral shift of the return beamand provides a signal to a processor that determines the distancebetween the backside of the substrate holder and the intersectionbetween the source beam and the return beam. Accordingly, the distancemeasuring device may measure a first actual distance at one stage of theplanarization process and then re-measure a second actual distance at asubsequent stage of the planarization process to determine the change inthickness of the substrate, the polishing rate of the substrate andseveral other performance parameters of the planarization process whilethe substrate is planarized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a conventionalchemical-mechanical polishing machine in accordance with the prior art.

FIG. 2 is a schematic cross-sectional view of an endpoint detector inaccordance with the invention.

FIG. 3 is a schematic cross-sectional view of a polisher with anendpoint detector in accordance with the invention.

FIG. 4 is a schematic cross-sectional view of a polisher with anendpoint detector in accordance with the invention.

FIG. 5 is a schematic cross-sectional view of a polisher with anendpoint detector in accordance with the invention.

FIG. 6 is a schematic cross-sectional view of a polisher with anendpoint detector in accordance with the invention.

FIG. 7 is a schematic cross-sectional view of another polishing machinewith a performance monitoring system in accordance with anotherembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed toward performance monitoring systems,such as an endpoint detector that quickly and accurately measures achange in wafer thickness of a semiconductor wafer or another type ofmicroelectronic substrate during chemical-mechanical polishing of thewafer. One aspect of the invention is to provide a reference platformupon which the wafer is positioned each time a measurement is taken.Another aspect of the invention is to provide a measuring face on thewafer carrier that may be engaged by a measuring device without removingthe wafer from either the reference platform or the wafer carrier. Aswill be discussed in greater detail below, by providing such a referenceplatform and a measuring face, the change in wafer thickness can bequickly and accurately measured while the wafer is attached to the wafercarrier and positioned on the reference platform. In addition tomeasuring the change in wafer thickness, certain embodiments ofperformance monitoring systems according to the invention may alsodetermine the actual elevation of the wafer carrier with respect to aknown elevation to monitor the endpoint, the polishing rate, and severalother performance parameters of CMP processes. Many specific details ofcertain embodiments of the invention are set forth in FIGS. 2-7 toprovide a thorough understanding of such embodiments. One skilled in theart, however, will understand that the present invention may haveadditional embodiments and may be practiced without several of thedetails described in the following detailed description of theinvention.

FIG. 2 illustrates an endpoint detector 50 used in a conventional CMPmachine in which a wafer 60 or another type of microelectronic substrateis mounted in a substrate holder or wafer carrier 30. The wafer carrier30 is typically attached to an actuator 36 that manipulates the wafercarrier 30. The endpoint detector 50 includes a reference platform 70, ameasuring face 80 on the wafer carrier 30, and a measuring device 90. Anupper surface 72 on the reference platform 70 is maintained at a fixeddistance from the measuring device 90 over all of the measurements of asingle wafer. The measuring face 80 is positioned on an upper face 38 ofthe wafer carrier 30 so that it is exposed to the measuring device 90when the wafer carrier 30 presses the wafer 60 against the referencesurface 70. The measuring face 80 is preferably a planar, reflectivesurface that is either the upper surface 38 of the wafer carrier itself,or a separate panel attached to the wafer carrier 80. The measuringdevice 90 engages the measuring face 80 to measure the displacement ofthe measuring face 80 with respect to the fixed position of themeasuring device 90.

In one embodiment, the measuring device is an interferometer with anemitter 92 and a receiver 94. The emitter directs a beam of light ontothe measuring face 80, which reflects the light beam back to thereceiver 94. As the distance between the measuring face 80 and themeasuring device 90 changes in correspondence to the change in thicknessof the wafer 60, the phase of the reflected light beam at the receiver94 changes accordingly. A controller 96 connected to the receiver 94translates the phase change of the reflected light beam into ameasurement of the vertical displacement of the measuring face 80 withrespect to the position of the measuring device 90. Importantly, boththe reference platform 70 and the measuring device 90 are fixed againstdisplacement with respect to each other to maintain a constant distancetherebetween over all of the measurements of a single wafer. Thedistance between the reference platform 70 and the measuring device 90,however, may change from one wafer to another. The endpoint detector 50,therefore, eliminates one variable of many conventional endpointtechniques that commonly produces inaccurate measurements of the changein thickness of the wafer 60.

In operation, the wafer carrier 30 initially places the wafer 60 on theupper surface 72 of the reference platform 70 before the wafer 60 ispolished. When the wafer 60 is initially placed on the referenceplatform 70, the measuring face 80 is positioned at a height h₁ withrespect to the measuring device 90. The emitter 92 then directs thelight beam 93 onto the measuring face 80 to determine a baselinemeasurement of the position of the measuring face 80 at the height h₁.After the baseline measurement is obtained, the wafer is polished for aperiod of time. The change in thickness of the wafer (Δt) is equal tothe distance between an original surface 62 of the wafer and a newsurface 62(a). The wafer 60 is then re-placed on the upper surface 72 ofthe reference platform 70, and the position of the measuring face 80accordingly changes to a height h₂. The light beam 93 from the measuringdevice 90 re-engages the measuring face 80 to measure the displacement(Δd) of the measuring face 80 at the height h₂. The displacement Δd ofthe measuring face 80 is proportional to, and may directly correspondto, the change in thickness Δt of the wafer 60.

One advantage of the endpoint detector 50 is that it provides highlyaccurate measurements of the change in thickness Δt of the wafer 60. Anaspect of the invention is that the distance is constant between theupper surface 72 of the reference platform 70 and the measuring device90 over all of the measurements of a single wafer. Accordingly, thedisplacement Δd of the measuring surface 80 is caused by the change inthickness Δt of the wafer 60. Moreover, by measuring the displacement ofthe measuring face 80, the wafer 60 does not need to overhang thereference platform 70 as in conventional techniques that directlyimpinge the wafer with a light beam. The endpoint detector 50,therefore, provides highly accurate measurements of the change inthickness Δt of the wafer 60.

FIG. 3 schematically illustrates a polishing machine 52 with an endpointdetector in accordance with the invention. In this embodiment, thereference platform 70 is the polishing pad 40. The upper surface 72 ofthe platform 70 is accordingly the upper surface of the polishing pad40. The wafer carrier 30 places the wafer 60 on the polishingpad/reference platform 70 to polish the wafer 60 and to measure thechange in thickness of the wafer 60. When the wafer carrier 30 ispositioned substantially under the measuring device, the measuringdevice 90 engages the measuring face 80. In operation, the change inthickness of the wafer is measured as described above with respect toFIG. 2. This embodiment of the invention is particularly useful forrigid pads or semi-rigid pads that compress substantially less than thechange in thickness of the wafer. However, even if the polishingpad/reference platform 70 is compressible, the measurements made by theendpoint detector of the polishing machine 52 will be accurate as longas any force exerted on the pad/platform 70 is the same for allmeasurements. The polishing machine 52 quickly measures the change inthickness of the wafer 60 because the wafer 60 is not removed fromeither the wafer carrier 30 or the polishing pad/reference platform 70.Therefore, this particular embodiment of the invention enhances thethroughput compared to conventional CMP processes.

FIGS. 4-6 illustrate several embodiments of polishing machines withendpoint detectors. FIG. 4 shows a polishing machine 54 with an endpointdetector in which the reference platform 70 is a separate pedestal 74that is fixed to the ground or the planarization machine. FIG. 5 shows apolishing machine 56 with an endpoint detector in which the referenceplatform 70 is spaced radially outwardly away from the polishing pad 40on the surface of the platen 20. In other related embodiments, areference platform 70(a) may be positioned in a hole 43 at the center ofthe pad 40, or the hole 43 can provide access to a reference platform70(b) defined by the center of the upper surface 22 of the platen 20.FIG. 6 shows a polishing machine 58 with an endpoint detector in whichthe reference platform 70 is attached to a wall 14 of the polishingmachine. In each of the polishing machines 54, 56, and 58, the change inthickness of the wafer 60 is measured by moving the wafer 60 from thepolishing pad 40 to the reference platform 70. The change indisplacement of the measuring face 80 is measured by engaging themeasuring face 80 with a light beam from the measuring device 90, asdescribed above with respect to FIG. 2.

An advantage of the polishing machines 52, 54, 56, and 58 is that theygenerally enhance the throughput of the CMP process. When the referenceplatform 70 is the polishing pad, the change in thickness Δt of thewafer 60 may be measured without removing the wafer 60 from the wafercarrier 30 or the polishing pad. Accordingly, the change in thickness Δtof the wafer 60 may be measured in situ with only minimal interruptionof the polishing of the wafer 60. When the platform 72 is separate fromthe polishing pad, the change in thickness Δt of the wafer 60 may bemeasured without removing the wafer 60 from the wafer carrier 30. Thus,the change in thickness Δt of the wafer may be measured with only aminor interruption to move the wafer between the polishing pad and thereference platform.

FIG. 7 is a schematic cross-sectional view of a CMP machine 110 inaccordance with another embodiment of the invention. The CMP machine 110may have a housing 112, a cavity 114 in the housing 112, and a barrier116 in the cavity 114. An actuator 126 attached to the housing 112 has ashaft 127 within the barrier 116 to support a plate or platen 120. Theactuator 126 may accordingly rotate the plate 120 via the shaft 127. Theplanarizing machine 110 also has a carrier assembly 130 attached to thehousing 112. In one embodiment, the carrier assembly 130 has a primaryactuator 131 that moves a first arm 132 vertically along a sweep axisP--P (arrow V) and rotates the arm 132 along the sweep axis P--P (arrowR₁). The arm 132 may carry a secondary actuator 134 with a drive shaft135 coupled to a substrate holder or wafer carrier 136. The substrateholder 136 preferably has a backside or upper face 138, a plurality ofnozzles 139 for dispensing a planarizing fluid 144, and a mounting siteto which a microelectronic substrate 12 may be attached. The substrate12, for example, may be a semiconductor wafer or a field emissiondisplay with or without integrated circuitry. The carrier assembly 130manipulates the substrate holder 136 to engage and translate thesubstrate 12 across a planarizing surface 142 of a planarizing medium140 (e.g., a polishing pad).

The carrier assembly 130 may also have a second arm 133 that rotatesabout the sweep axis P--P (arrow R₂). The first and second arms 132 and133 are preferably independently operable from another. The first arm132 may be coupled to the primary actuator 131 to be moved with respectto the sweep axis P--P as set forth above. The second arm 133 may have avertical portion that telescopes from the vertical portion of the firstarm 132. The second arm 133 may be independently coupled to a secondaryactuator 131a on the planarizing machine 110. The secondary actuator131a may accordingly move the second arm 133 about the sweep axis P--Pat a fixed or known elevation as the first arm 132 independently moveswith respect to the sweep axis P--P. For example, as the first arm 132moves vertically and rotationally about the sweep axis P--P to planarizethe substrate 12, the second arm 133 may rotate about the sweep axisP--P with the first arm 132 at a constant elevation.

The planarizing machine 110 may also have a performance monitoringsystem 190 attached to the second arm 133. The performance monitoringsystem 190 may be a non-contact distance measuring device 191 ("distancedevice") with a beam emitter 192, a reflector 193 spaced apart from thebeam emitter 192, and a detector 194. The beam emitter 192 projects abeam 195 (indicated in FIG. 7 by reference numbers 195a-c) to determinethe actual elevation of the substrate holder 136. As schematically shownin FIG. 7, the beam emitter 192 may project an initial portion of asource beam 195a toward the reflector 193. The reflector 193 is inclinedat an angle α that directs an intermediate portion of the source beam195b to the backside 138 of the substrate holder 136 so that a detector194 receives a return beam 195c. The detector 194 receives the returnbeam 195c and optically detects the lateral position "L" of the returnbeam 195c with respect to a scale (not shown) in the detector 194. Byknowing the angle α to maintain an isosceles triangle and the distance"Y" along the initial source beam 195a between the apex of the triangleand the reflector, a processor 198 operatively coupled to the distancedevice 191 determines the actual distance "d" between the backside 138of the substrate holder 136 and the initial portion of the source beam195a. Accordingly, the distance device 191 measures the actual elevationof the backside 138 of the substrate holder 136.

The distance device 191 is preferably a triangular displacement meterthat accurately measures the distance between the known elevation andthe backside 138 of the substrate holder 136. The beam emitter 192 mayaccordingly be a laser, and the beam 195 may accordingly be a laserbeam. One suitable laser displacement meter is the LC3 displacementmeter manufactured by Keyence Corporation of Woodcliff Lake, N.J.

In operation, the distance device 191 directs the beam 195 against thebackside 138 of the substrate holder 136 as the carrier assembly 130presses the substrate 12 against the planarizing medium 140. In someapplications, the distance measuring device 191 directs the beam 195against the backside 138 of the substrate holder 136 while the substrateholder 136 and the planarizing medium 140 are stationary. In otherapplications, the distance measuring device 191 directs the beam 195against the substrate holder 136 while imparting relative motion betweenthe substrate holder 136 and the planarizing medium 140. For example,the distance device 191 and the substrate holder 136 may rotate togetherabout the sweep axis P--P during the planarization process so that thebeam 195 continuously impinges the backside 138 of the substrate holder136. In another embodiment, the distance device 191 may be positioned ata fixed point along the planarizing path of the substrate holder 136 sothat the beam 195 periodically impinges the backside 138 of thesubstrate holder 136 during the planarization process. In either case,the distance device 191 detects the elevation of the backside of thesubstrate holder 136 with respect to the known elevation by measuring afirst actual distance at one stage of the planarization process and byre-measuring a second actual distance at a subsequent stage. Asexplained in more detail below, the distance between the known elevationand the backside 138 of the substrate holder 136 provides data tomonitor the performance of the planarization process.

In one particular application, the performance monitoring system 190 ofthe planarizing machine 110 may detect the endpoint of the planarizationprocess. During the planarization process as the carrier assembly 30moves the substrate 12 across the planarizing medium 140, the distancedevice 191 measures the elevation of the backside 138 of the substrateholder 136. When the change in elevation of the substrate holder 136 iswithin a range of the desired change in thickness of the substrate 12,the planarizing machine 110 terminates the removal of material from thesubstrate 12. For example, the planarizing machine 110 may terminate theprocess by disengaging the substrate 12 from the planarizing medium 140or stopping the relative motion between the substrate 12 and theplanarizing medium 140.

The performance monitoring system 190 may also monitor other systemparameters to indicate when the planarization process is not operatingat a desired level. For example, the processor 198 may determine thepolishing rate of the substrate 12 without interrupting the planarizingcycle by correlating the change in elevation of the substrate holder 136with the elapsed time of the cycle. A significant change in thepolishing rate generally indicates that one of the planarizingparameters is not operating within a desired range. A drop in thepolishing rate, for example, may indicate that the condition of thepolishing pad has deteriorated such that the pad does not uniformlyremove material from the substrate. A significant change in thepolishing rate may also indicate that another polishing parameter is notwithin a desired operating range. Therefore, the planarizing machine 110may also monitor other system parameters to indicate whether theplanarization process is operating within a desired range.

In still another application, the performance monitoring systems 190 maymeasure the vertical motion of the substrate holder to determine whetheranomalies occur in the vertical displacement pattern of the substrateholder. In most CMP applications, the substrate holder 136 is attachedto the shaft 137 by a gimbal joint. Accordingly, even though thesubstrate holder 136 should desirably remain level during planarization,most substrate holders have a pattern of small vertical displacementunder normal operating conditions. The distance device 191 can alsomeasure and indicate the vertical displacement pattern of the substrateholder 136 during planarization. Accordingly, if the verticaldisplacement pattern changes or large anomalies occur, it may indicatethat the pad surface, the slurry distribution or the substrate surfaceis not within a normal operating range. Therefore, the planarizingmachine 110 also provides another source of information for monitoringthe planarizing characteristics of the planarization process.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

What is claimed is:
 1. In the manufacturing of microelectronic devices,a method of detecting the endpoint in a planarization process forremoving material from a microelectronic device substrate in a substrateholder, comprising:detecting an elevation of a backside of the substrateholder as the substrate in the substrate holder engages a planarizingmedium by contemporaneously imparting relative motion between thesubstrate and the planarizing medium and measuring an elevation of thebackside of the substrate holder from a known elevation, whereinmeasuring an elevation of the substrate holder comprises measuring afirst actual distance between the backside of the substrate holder andthe known elevation at one stage of the planarization process, andre-measuring a second actual distance between the backside of thesubstrate holder and the known elevation at another stage of theplanarization process, and wherein measuring the first actual distanceand re-measuring the second actual distance comprisesprojecting aninitial portion of a source beam from a beam emitter toward a reflector;directing an intermediate portion of the source beam from the reflectorto reflect from the backside of the substrate holder so that a returnbeam reflecting from the backside of the substrate holder is received bya detector; observing a position of a return beam reflecting from thebackside of the substrate holder with the detector, the position of thereturn beam with respect to the detector and the angle of the reflectormeasuring an actual distance between the known elevation and thebackside of the wafer; and moving the beam emitter, the reflector andthe detector with the substrate holder as the substrate holder moves thesubstrate across the planarizing medium to continuously detect theelevation of the backside of the substrate with respect to the knownelevation, the first actual distance being measured at one stage in theplanarizing process and the second actual distance being re-measured ata subsequent stage in the planarizing process; and terminating theremoval of material from the substrate when the detected elevationchanges by a distance approximately equal to a desired change inthickness of the wafer.
 2. In the manufacturing of microelectronicdevices, a method of detecting the endpoint in a planarization processfor removing material from a microelectronic substrate in a substrateholder, comprising:measuring a first actual distance between thebackside of a substrate holder and a known elevation above the substrateholder as the substrate in the substrate holder engages the planarizingmedium at one stage of the planarization process; re-measuring a secondactual distance between the backside of the substrate holder and theknown elevation as the substrate in the substrate holder engages theplanarizing medium at another stage of the planarization process,wherein measuring the first actual distance and re-measuring the secondactual distance comprisesprojecting an initial portion of a source beamfrom a beam emitter toward a reflector; directing an intermediateportion of the source beam from the reflector to reflect from thebackside of the substrate holder so that a return beam reflecting fromthe backside of the substrate holder is received by a detector;observing a position of a return beam reflecting from the backside ofthe substrate holder with the detector, the position of the return beamwith respect to the detector and the angle of the reflector measuring anactual distance between the known elevation and the backside of thewafer; and moving the beam emitter, the reflector and the detector withthe substrate holder as the substrate holder moves the substrate acrossthe planarizing medium to continuously detect the elevation of thebackside of the substrate with respect to the known elevation, the firstactual distance being measured at one stage in the planarizing processand the second actual distance being re-measured at a subsequent stagein the planarizing process; and terminating the removal of material fromthe substrate when the difference between the first and second actualdistances is within a desired change in thickness of the substrate. 3.In the manufacturing of microelectronic devices, a method ofplanarization a microelectronic substrate in a substrate holder,comprising:imparting relative motion between a planarizing medium andthe substrate engaged with the planarizing medium to remove materialfrom a surface of the substrate; measuring a first actual distancebetween a backside of the substrate holder and a known elevation abovethe substrate holder as the substrate in the substrate holder engagesthe planarizing medium at one stage of the planarization process;re-measuring a second actual distance between the backside of thesubstrate holder and the known elevation as the substrate in thesubstrate holder engages the planarizing medium at another stage of theplanarization process, wherein measuring the first actual distance andre-measuring the second actual distance comprisesprojecting an initialportion of a source beam from a beam emitter toward a reflector;directing an intermediate portion of the source beam from the reflectorto reflect from the backside of the substrate holder so that a returnbeam reflecting from the backside of the substrate holder is received bya detector; observing a position of a return beam reflecting from thebackside of the substrate holder with the detector, the position of thereturn beam with respect to the detector and the angle of the reflectormeasuring an actual distance between the known elevation and thebackside of the wafer; and moving the beam emitter, the reflector andthe detector with the substrate holder as the substrate holder moves thesubstrate across the planarizing medium to continuously detect theelevation of the backside of the substrate with respect to the knownelevation, the first actual distance being measured at one stage in theplanarizing process and the second actual distance being re-measured ata subsequent stage in the planarizing process; and terminating theremoval of material from the substrate when the difference between thefirst and second actual distances is within a desired change inthickness of the substrate.
 4. In the manufacturing of microelectronicdevices, a method of monitoring performance of a planarization processfor removing material from a microelectronic device substrate in asubstrate holder, comprising:measuring an elevation of a backside of thesubstrate holder as the substrate in the substrate holder engages aplanarizing medium by contemporaneously imparting relative motionbetween the substrate and the planarizing medium to simultaneouslyremove material from a surface of the substrate and measuring a distancebetween a known elevation and the backside of the substrate holder; andevaluating whether a performance characteristic of the planarizationprocess is within an acceptable range based upon the measured elevationof the substrate holder wherein the planarizing characteristic is avertical motion of the substrate holder during planarization andevaluating the vertical motion comprisesdetermining a verticaldisplacement pattern of the substrate holder according to the measuredelevation of the substrate holder during planarization; assessingwhether the vertical displacement pattern of the substrate holder hasanomalies; and interrupting the planarizing process when an anomalyoccurs in the vertical displacement pattern.
 5. A planarizing machinefor planarizing microelectronic substrates, comprising:a flat plate; aplanarizing medium having a planarizing surface, the planarizing mediumbeing fastened to the plate; a carrier assembly having a supportstructure including a first arm that rotates about a sweep axis normalto the plate and a second arm above the first arm, and the carrierassembly further having a substrate holder attached to the first arm tosweep across the planarizing medium along a planarizing path, thesubstrate holder having a mounting site facing the planarizing medium tocarry a microelectronic substrate and a backside facing away from theplanarizing medium, the carrier assembly moving the substrate holder toselectively engage the substrate with the planarizing medium, and atleast one of the substrate holder and the planarizing medium beingmovable to translate the substrate with respect to the planarizingsurface; and a non-contact distance measuring device positioned over thebackside of the substrate holder for at least a portion of the time thatthe substrate in the substrate holder engages the planarizing surface,the non-contact measuring device being at a known elevation with respectto the plate, and the non-contact measuring device measuring an actualdistance between the backside of the substrate holder and the knownelevation during planarization of the substrate on the planarizingsurface, wherein the non-contact distance measuring device comprises atriangulation distance measuring meter having a beam emitter to projectan initial portion of a source beam, a reflector to direct anintermediate portion of the source beam to the backside of the substrateholder so that a return beam reflects from the substrate holder, adetector to determine a lateral shift of the return beam, and aprocessor to compute the distance between the initial portion of thesource beam and the backside of the wafer, and wherein the distancemeasuring device is attached to the second arm above the planarizingpath to impinge the beam against the backside of the substrate holder asthe substrate holder engages the substrate with the planarizing mediumand relative motion occurs between the substrate and the planarizingmedium.
 6. The planarizing machine of claim 5 wherein the second arm isalso rotatable about the sweep axis, and wherein the first and secondarms are coupled to an actuator to rotate together about the sweep axisso that the distance measuring device continuously impinges the beamagainst the backside of the substrate holder along the planarizing path.7. The planarizing machine of claim 5 wherein the first arm is coupledto an actuator to sweep the substrate across the planarizing path andthe second remains stationary with respect to the sweep axis so that thedistance measuring device periodically impinges the beam against thebackside of the substrate holder when the substrate holder is beneaththe distance measuring device.
 8. A planarizing machine for planarizingmicroelectronic substrates, comprising:a flat plate; a planarizingmedium having a planarizing surface, the planarizing medium beingfastened to the plate; a carrier assembly having a support structureincluding a first arm that rotates about a sweep axis normal to theplate and a second arm above the first arm, and the carrier assemblyfurther having a substrate holder attached to the first arm to sweepacross the planarizing medium along a planarizing path, the substrateholder having a mounting site facing the planarizing medium to carry amicroelectronic substrate and a backside facing away from theplanarizing medium, the carrier assembly moving the substrate holder toselectively engage the substrate with the planarizing medium, and atleast one of the substrate holder and the planarizing medium beingmovable to translate the substrate with respect to the planarizingsurface; and a distance measuring device attached to the planarizingmachine, the distance measuring device having a beam emitter positionedat a known elevation with respect to the plate to project an initialportion of a source beam at a reflector that directs an intermediateportion of the source beam against the backside of the substrate holderduring planarization, and a primary detector to receive a return beamreflecting from the backside of the substrate holder, the primarydetector monitoring a lateral shift of the return beam to determine theactual distance between the backside of the substrate holder and theinitial portion of the source beam as the substrate is planarized,wherein the distance measuring device is attached to the second armabove the planarizing path to impinge the beam against the backside ofthe substrate holder as the substrate holder engages the substrate withthe planarizing medium and relative motion occurs between the substrateand the planarizing medium.
 9. The planarizing machine of claim 8wherein the second arm is also rotatable about the sweep axis, andwherein the first and second arms are coupled to an actuator to rotatetogether about the sweep axis so that the distance measuring devicecontinuously impinges the beam against the backside of the substrateholder along the planarizing path.
 10. The planarizing machine of claim8 wherein the first arm is coupled to an actuator to sweep the substrateacross the planarizing path and the second remains stationary withrespect to the sweep axis so that the distance measuring deviceperiodically impinges the beam against the backside of the substrateholder when the substrate holder is beneath the distance measuringdevice.